linux-kernel - [PATCH] MIPS: Enable interrupts before WAIT instruction.

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Date:	Thu,  2 May 2013 13:48:12 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	linux-mips@...ux-mips.org, ralf@...ux-mips.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, David Daney <david.daney@...ium.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jonas Gorski <jogo@...nwrt.org>
Subject: [PATCH] MIPS: Enable interrupts before WAIT instruction.

From: David Daney <david.daney@...ium.com>

As noted by Thomas Gleixner:

   commit cdbedc61c8 (mips: Use generic idle loop) broke MIPS as I did
   not realize that MIPS wants to invoke the wait instructions with
   interrupts enabled.

Instead of enabling interrupts in arch_cpu_idle() as Thomas' initial
patch does, we follow Linus' suggestion of doing it in the assembly
code to prevent the compiler from rearranging things.

Signed-off-by: David Daney <david.daney@...ium.com>
Reported-by: EunBong Song <eunb.song@...sung.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Jonas Gorski <jogo@...nwrt.org>
---

This is only very lightly tested, we need more testing before
declaring it the definitive fix.

 arch/mips/kernel/genex.S | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
index ecb347c..57cda9a 100644
--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -132,12 +132,13 @@ LEAF(r4k_wait)
 	.set	noreorder
 	/* start of rollback region */
 	LONG_L	t0, TI_FLAGS($28)
-	nop
 	andi	t0, _TIF_NEED_RESCHED
 	bnez	t0, 1f
 	 nop
-	nop
-	nop
+	/* Enable interrupts so WAIT will complete */
+	mfc0	t0, CP0_STATUS
+	ori	t0, ST0_IE
+	mtc0	t0, CP0_STATUS
 	.set	mips3
 	wait
 	/* end of rollback region (the region size must be power of two) */
-- 
1.7.11.7

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